Semiconductor device manufacturing system for etching a semiconductor by plasma discharge

ABSTRACT

A semiconductor device manufacturing system has a vacuum chamber which is provided with a cathode electrode for holding a substrate to be processed and into which a reactive gas for generating discharging plasma by the application of a high-frequency electric power is introduced, a measuring circuit which measures at least one of the impedance of a system including the plasma, the peak-to-peak voltage of a high-frequency signal applied to the plasma, and a self-bias voltage applied to the cathode electrode, and a sense circuit which compares the measured value from the measuring circuit with previously prepared data and senses the change of processing characteristics with time for the substrate in using the discharging plasma or the cleaning time of the inside of the vacuum chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 11-076352, filed Mar. 19,1999, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] This invention relates to a semiconductor device manufacturingsystem, and more particularly to a system for processing a semiconductorsubstrate by plasma discharge used in, for example, a reactive ionetching (RIE) system with a high-frequency power supply.

[0003] In a dry etching system used in the process of manufacturingsemiconductor devices, a substrate on whose surface a given mask patternhas been formed is placed in a vacuum reactive chamber. A reactive gasis introduced into the vacuum reactive chamber and at the same time,discharging plasma is generated, thereby causing reactive ions to etchthe substrate.

[0004] At that time, high-vapor-pressure reaction products are generallyproduced as a result of the reaction between the reactive ions and theetched layer. The reaction products are exhausted. Depending on thepressure in the vacuum chamber, the type of reactive gas, the flow rate,and the amount of energy of the reactive ions, the rate of reaction withthe etched film and the types of reaction products differ.

[0005] In a system for processing a semiconductor substrate by plasmadischarge, one means for clearly verifying the presence or absence ofthe change of processing conditions with time and the degree of thechange with time, if any, is to process a substrate in such a mannerthat it has a shape with a high aspect ratio.

[0006] The shape with a high aspect ratio is, for example, a contacthole, a via hole, or a trench. As a typical example, problemsencountered in a case where a conventional dry etching system is used inthe process of forming trenches for trench capacitors in the memorycells of, for example, a DRAM will be explained.

[0007]FIGS. 1A and 1B are sectional views of a substrate in the processof forming a trench for trench capacitor.

[0008] As shown in FIG. 1A, a TEOS (Tetraethyl orthosilicate) film 12 isfirst formed on an Si substrate 11 to be processed. Then, patterning isdone to form a mask pattern, thereby forming a sample of the substrate.

[0009] Next, after each lot processing of semiconductor substrates by amagnetron RIE system, a sample of the substrate as shown in FIG. 1A isplaced in a vacuum reactive chamber. Reactive gases HBr, O₂, and NF₃ areintroduced into the vacuum reactive chamber at flow rates of 100, 10,and 70 sccm, respectively. Then, plasma discharge is effected at apressure of about 200 mTorr (about 26.6 Pa) with a high-frequency powersupply output of about 1000 W, thereby causing reactive ions to etch thesample.

[0010] As a result of this, a trench 13 for trench capacitor is formedat the Si substrate 11 as shown in FIG. 1B. Here, θ is the taper angleat the top of the trench 13 and D is the diameter of the bottom of thetrench.

[0011]FIG. 2 shows the relationship between the number of lots ofsubstrates processed by a conventional RIE system and the diameter D(μm) of the trench bottom. The number of substrates processed in one lotis, for example, 24 to 25.

[0012] As seen from FIG. 2, as the number of substrates processedincreases, the diameter D of the trench bottom decreases. The reason isthat, as the number of substrates processed increases, the degree of thetaper at the top of the trench decreases, making the taper angle θsmaller gradually.

[0013] The cause of this is not clear, but the following phenomenon isconsidered to be taking place.

[0014] In processing a trench for trench capacitor, SiBr_(x),SiBr_(y)O_(z), and SiF_(α) are mainly produced as reaction products.Although most of them are exhausted, part of them adhere to therelatively low-temperature parts of the vacuum chamber or decomposeagain into substances with lower vapor pressures and adhere to theinside of the vacuum chamber.

[0015] These deposits are estimated to be of the SiO₂ family. When thedeposits build up to form a film, they are exposed to degassing orplasma, which causes the film to decompose again. As a result, theactual flow rate of each process gas in the atmosphere in the vacuumchamber differs from the set flow rate, preventing the desired shape andetching rate from being achieved.

[0016] As described above, because the diameter of the trench bottom isclosely related to the condition of the deposited film on the inside ofthe vacuum chamber, a grasp of the condition of the deposited film wouldhelp determine the time the inside of the vacuum chamber should becleaned. It is, however, impossible to grasp the condition of the innersurface of the vacuum chamber from the outside.

[0017] At present, the standard value of the diameter D of the trenchbottom for trench capacitor is 0.1 μm. In this situation, the vacuumchamber is opened to atmosphere and cleaned manually every, for example,eight lots on the basis of the data in FIG. 2. However, it is not clearwhether the method is the best.

[0018] As described above, with the conventional dry etching system formanufacturing semiconductor devices, it is impossible to externallygrasp the condition of the inner surface and others of the vacuumchamber. For example, in processing a trench for trench capacitor, thechange of the diameter of the trench bottom with time dependent on thenumber of substrates processed is impossible to grasp and therefore thesuitable cleaning time of the inside of the vacuum chamber cannot bedetermined.

BRIEF SUMMARY OF THE INVENTION

[0019] It is, accordingly, an object of the prevention is to provide asemiconductor device manufacturing system which enables the change ofthe diameter of the trench bottom with time dependent on the number ofsubstrates processed in processing a trench and the condition of theinner surface and others of the vacuum chamber to be grasped from theoutside, making it possible to determine the suitable cleaning time ofthe inner surface of the vacuum chamber and control the processing ofthe shape of a substrate, which thereby suppresses the change with time.

[0020] According to a first aspect of the present invention, there isprovided a semiconductor device manufacturing system comprising: avacuum chamber provided with a cathode electrode for holding a substrateto be processed and into which a reactive gas for generating dischargingplasma by the application of a high-frequency electric power isintroduced; a high-frequency power supply connected to the cathodeelectrode, for applying a high-frequency electric power to the cathodeelectrode; a measuring circuit connected to the cathode electrode, formeasuring at least one of the impedance of a system including theplasma, the peak-to-peak voltage of a high-frequency signal applied tothe plasma, and a self-bias voltage applied to the cathode electrode;and a sense circuit for receiving the measured value from the measuringcircuit, and for sensing the change of processing characteristics withtime for the substrate in using the discharging plasma by comparing themeasured value with previously prepared data.

[0021] According to a second aspect of the present invention, there isprovided a semiconductor device manufacturing system comprising: avacuum chamber provided with a cathode electrode for holding a substrateto be processed and into which a reactive gas for generating dischargingplasma by the application of a high-frequency electric power isintroduced; a high-frequency power supply connected to the cathodeelectrode, for applying a high-frequency electric power to the cathodeelectrode; a measuring circuit connected to the cathode electrode, formeasuring at least one of the impedance of a system including theplasma, the peak-to-peak voltage of a high-frequency signal applied tothe plasma, and a self-bias voltage applied to the cathode electrode;and a control circuit for receiving the measured value from themeasuring circuit, for supplying an output based on the measured valueto the high-frequency power supply, and for controlling the output ofthe high-frequency power supply in such a manner that the measured valueof the measuring circuit is kept at a specific value.

[0022] According to a third aspect of the present invention, there isprovided a semiconductor device manufacturing system comprising: avacuum chamber provided with a cathode electrode for holding a substrateto be processed and a reactive gas intake and into which a reactive gasfor generating discharging plasma by the application of a high-frequencyelectric power is introduced through the intake; a high-frequency powersupply connected to the cathode electrode, for applying a high-frequencyelectric power to the cathode electrode; a valve provided at the intakein such a manner that the intake of the reactive gas introduced into thevacuum chamber is controlled; a measuring circuit connected to thecathode electrode for measuring at least one of the impedance of asystem including the plasma, the peak-to-peak voltage of ahigh-frequency signal applied to the plasma, and a self-bias voltageapplied to the cathode electrode; and a control circuit for receivingthe measured value from the measuring circuit, for supplying an outputbased on the measured value to the valve, and for controlling theoperation of the valve in such a manner that the measured value of themeasuring circuit is kept at a specific value.

[0023] According to a fourth aspect of the present invention, there isprovided a semiconductor device manufacturing system comprising: avacuum chamber provided with a cathode electrode for holding a substrateto be processed and into which a reactive gas for generating dischargingplasma by the application of a high-frequency electric power isintroduced; a high-frequency power supply connected to the cathodeelectrode, for applying a high-frequency electric power to the cathodeelectrode; a measuring circuit for measuring at least one of theimpedance of a system including the plasma, the peak-to-peak voltage ofa high-frequency signal applied to the plasma, and a self-bias voltageapplied to the cathode electrode; and a report circuit for receiving themeasured value from the measuring circuit, for sensing that the measuredvalue has departed from a preset range, and for reporting the cleaningtime of the inside of the vacuum chamber.

[0024] According to a fifth aspect of the present invention, there isprovided a semiconductor device manufacturing system comprising: avacuum chamber provided with a cathode electrode for holding a substrateto be processed, a reactive gas intake, and a reactive gas outlet, andinto which a reactive gas for generating discharging plasma by theapplication of a high-frequency electric power is introduced through theintake; a high-frequency power supply connected to the cathodeelectrode, for applying a high-frequency electric power to the cathodeelectrode; an electronic valve provided at the outlet in such a mannerthat the pressure in the vacuum chamber is adjusted; a measuring circuitconnected to the cathode electrode for measuring at least one of theimpedance of a system including the plasma, the peak-to-peak voltage ofa high-frequency signal applied to the plasma, and a self-bias voltageapplied to the cathode electrode; and a control circuit for receivingthe measured value from the measuring circuit, for supplying an outputbased on the measured value to the valve, and for controlling theoperation of the valve in such a manner that the measured value of themeasuring circuit is kept at a specific value.

[0025] According to a sixth aspect of the present invention, there isprovided a semiconductor device manufacturing system comprising: avacuum chamber provided with a cathode electrode for holding a substrateto be processed and into which a reactive gas for generating dischargingplasma by the application of a high-frequency electric power isintroduced; a high-frequency power supply connected to the cathodeelectrode, for applying a high-frequency electric power to the cathodeelectrode; a cooling gas carrying path provided at the cathode electrodeand into which a cooling gas is introduced to cool the substrate; anelectronic valve provided at the cooling gas carrying path in such amanner that the pressure of the cooling gas introduced into the coolinggas carrying path is adjusted; a measuring circuit connected to thecathode electrode, for measuring at least one of the impedance of asystem including the plasma, the peak-to-peak voltage of ahigh-frequency signal applied to the plasma, and a self-bias voltageapplied to the cathode electrode; and a control circuit for receivingthe measured value from the measuring circuit, for supplying an outputbased on the measured value, and for controlling the operation of thevalve in such a manner that the measured value of the measuring circuitis kept at a specific value.

[0026] Additional objects and advantages of the invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention may be realized and obtained bymeans of the instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0027] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate presently preferredembodiments of the invention, and together with the general descriptiongiven above and the detailed description of the preferred embodimentsgiven below, serve to explain the principles of the invention.

[0028]FIGS. 1A and 1B are sectional views of a substrate in the processof forming a trench for trench capacitor;

[0029]FIG. 2 shows the relationship between the number of substratesprocessed and the diameter of the trench bottom in a conventional dryetching system;

[0030]FIG. 3 is a schematic block diagram showing the configuration ofan RIE system according to a first embodiment of the present inventionand its peripheral circuit;

[0031]FIG. 4A shows the relationship between the number of lots ofsubstrates processed, the peak-to-peak voltage of a high-frequencysignal, and the diameter of the trench bottom in the system of FIG. 3;

[0032]FIG. 4B shows the relationship between the peak-to-peak voltage ofthe high-frequency signal and the diameter of the trench bottom in thesystem of FIG. 3;

[0033]FIG. 5 is a schematic block diagram showing the configuration ofan RIE system according to a second embodiment of the present inventionand its peripheral circuit;

[0034]FIG. 6A shows the relationship between the output of ahigh-frequency power supply and the peak-to-peak voltage of thehigh-frequency signal in the system of FIG. 5;

[0035]FIG. 6B shows the relationship between the peak-to-peak voltage ofthe high-frequency signal and the taper angle θ at the top of the trenchin the system of FIG. 5;

[0036]FIG. 7 is a schematic block diagram showing the configuration ofan RIE system according to a third embodiment of the present inventionand its peripheral circuit;

[0037]FIG. 8A shows the relationship between the flow rate of a reactivegas and the peak-to-peak voltage of a high-frequency signal in thesystem of FIG. 7;

[0038]FIG. 8B shows the relationship between the peak-to-peak voltage ofthe high-frequency signal and the taper angle at the top of the trenchin the system of FIG. 7;

[0039]FIG. 9 is a flowchart to help explain a method of manufacturingsemiconductor devices using the system of FIG. 5 or 7;

[0040]FIG. 10 is a schematic block diagram showing the configuration ofan RIE system according to a fourth embodiment of the present inventionand its peripheral circuit;

[0041]FIG. 11 shows the relationship between the pressure in the vacuumreactive chamber and the taper angle θ at the top of the trench in thesystem of FIG. 10;

[0042]FIG. 12 is a schematic block diagram showing the configuration ofan RIE system according to a fifth embodiment of the present inventionand its peripheral circuit; and

[0043]FIG. 13 shows the relationship between the pressure of a coolinggas to adjust the temperature of the substrate to be processed and thetaper angle at the top of the trench in the system of FIG. 12.

DETAILED DESCRIPTION OF THE INVENTION

[0044] Hereinafter, referring to the accompanying drawings, embodimentsof the present invention will be explained. The same reference symbolsdesignate the corresponding parts throughout all the views andrepetitious explanation will be avoided.

[0045]FIG. 3 shows a magnetron RIE system, a type of dry etching systemaccording to a first embodiment of the present invention, and a controlcircuit for controlling the operation of the system.

[0046] In FIG. 3, numeral 20 indicates an RIE system. The RIE system 20is provided with a vacuum reactive chamber 21. In the vacuum reactivechamber 21, a cathode electrode 23 for holding a substrate to beprocessed is provided. When a high-frequency power supply, explainedlater, applies a high-frequency electric power to the cathode electrode23 and a reactive gas is introduced, discharging plasma 24 developsinside the vacuum reactive chamber 21. In the vacuum reactive chamber21, a gas intake 25 for introducing a reactive gas and an outlet 26 forexhausting the gas from the vacuum reactive chamber 21 are provided.Three branch paths 27, 28, 29 are provided at the gas intake 25. When amixed gas of three types of gases, for example, HBr, O₂, and NF₃, isused as etching gas, these three types of gases are carried through thethree branch paths 27, 28, 29. In the branch paths 27, 28, 29,electronic valves 30, 31, 32 for adjusting the flow rate of the gasesare provided respectively. At the outlet 26, there is provided anelectronic valve 33 for controlling the amount of exhaust to adjust thepressure in the vacuum reactive chamber 21.

[0047] A high-frequency power supply 34 including, for example, amagnetron is connected to the cathode electrode 23. The output of thehigh-frequency power supply 34 is supplied to the cathode electrode 23.An impedance matching circuit (or matching controller) 35 is providedbetween the high-frequency power supply 34 and the cathode electrode 23.The matching controller 35 is for effecting the impedance matchingbetween the output of the high-frequency power supply 34 and the loadside.

[0048] The matching controller 35 is composed of, for example, twovariable capacitors 36, 37, and an inductance 38. The values of the twovariable capacitors 36, 37 are controlled automatically by an automaticcontrol loop (not shown) in such a manner that the reflected powerreturning to the high-frequency power supply 34 always becomes thesmallest, thereby achieving impedance matching.

[0049] Further connected to the cathode electrode 23 are a Vpp measuringcircuit 39 for measuring the peak-to-peak voltage Vpp of ahigh-frequency signal applied to the plasma 24, a Vdc measuring circuit40 for measuring a self-bias voltage Vdc applied to the cathodeelectrode 23, and an impedance (Z) measuring circuit 41 for measuringthe impedance (Z) of a system including the plasma 24.

[0050] Then, the voltage Vpp measured at the Vpp measuring circuit 39,the voltage Vdc measured at the Vdc measuring circuit 40, and theimpedance (Z) measured at the impedance measuring circuit 41 areinputted to a sense/report circuit 42. The sense/report circuit 42 hasthe function of comparing the outputs (or measurements) of the Vppmeasuring circuit 39, the Vdc measuring circuit 40, and the impedancemeasuring circuit 41 with previously prepared data, sensing the changeof processing characteristics with time for the substrate 22 to beprocessed, and determining and reporting the cleaning time of the insideof the vacuum chamber 21, and outputs a sense signal and a reportsignal.

[0051] The matching controller 35 is so controlled that the total ofimpedance as a physical quantity to be monitored is, for example, 50° inthe part including the matching controller 34 and beyond that whenviewed from the high-frequency power supply 34, that is, the systemincluding the plasma on the vacuum reactive chamber 21 side. Forexample, if the impedance of the system including the plasma is 30°, thevalues of the two capacitors 36, 37 are adjusted by the automaticcontrol loop so that the impedance of the matching controller 35 itselfmay be 20°. Since the impedance of the system including the plasmavaries, depending on the etching condition of the substrate in etchingthe substrate or the change of the state in the vacuum reactive chamber21, it is possible to control of the shape of the substrate and graspthe buildup of the deposited film on the inner surface of the vacuumreactive chamber 21 on the basis of the result of monitoring theimpedance of the system including the plasma.

[0052] Ordinary lot processing was done using the RIE system in FIG. 3.After each lot process, a sample of the substrate as shown in FIG. LAwas placed in the vacuum reactive chamber 21. HBr gas, O₂ gas, and NF₃gas were introduced as reactive gases into the vacuum reactive chamberat flow rates of about 100, 10, and 70 sccm, respectively. Dischargingplasma 24 was generated at a pressure of about 200 mToor (about 26.6 Pa)in the vacuum reactive chamber with the high-frequency power supply 34outputting about 1000 W, thereby causing reactive ions to etch thesample. As a result, a trench 13 for trench capacitor was formed in theSi substrate 11 as shown in FIG. 1B.

[0053] At that time, the relationship between the number of lots ofsubstrates processed and the diameter D of the trench bottom in the RIEsystem was examined. In addition, the relationship between the number oflots processed and the peak-to-peak voltage Vpp of a high-frequencysignal applied to the cathode electrode 23 in the vacuum reactivechamber was examined. The results of these are shown in FIG. 4A.

[0054] Examinations as described above were made several times using thesame mask pattern under the same etching conditions. FIG. 4B shows theresult of examining the relationship between the peak-to-peak voltageVpp of the high-frequency signal at that time and the diameter D of thetrench bottom.

[0055] It can be seen from FIGS. 4A and 4B that there is a correlationbetween the diameter D of the trench bottom and the peak-to-peak voltageVpp of the high-frequency signal and the diameter D of the trench bottomcan be almost determined by measuring the Vpp with the Vpp measuringcircuit 39.

[0056] As described above, the reason why the diameter D of the trenchbottom correlates with the peak-to-peak voltage Vpp of thehigh-frequency signal is not clear, but can be considered as follows.

[0057] When the shape of the trench has got thinner for some reason, theopening area of the Si substrate to be etched decreases. Because themain reaction products are estimated to be SiBr_(x), SiBr_(y)O_(z),SiF_(α), and the like, as the amount of Si in the substance to be etcheddecreases, the amount of reaction products decreases accordingly. As aresult, the frequency of collision between ions and reaction productsdecreases, resulting in a decrease in the impedance of the systemincluding the plasma 24. If the output of the high-frequency powersupply is W, the equation W=Vpp²/Z holds. In this case, because W isconstant (in this embodiment, about 1000 W), Vpp is also expected todecrease.

[0058] Between the self-bias voltage Vdc applied to the cathodeelectrode 23 holding the substrate 22 and the peak-to-peak voltage Vppof the high-frequency signal, the fact that Vdc is almost equal to Vpp/2is generally true. As a result, it is easily estimated that the diameterD of the trench bottom is determined by measuring the Vdc with the Vdcmeasuring circuit 40 as is the Vpp.

[0059] With the RIE system of the first embodiment, there is providedthe sense/report circuit 42 that compares the outputs (measurements) ofthe measuring circuits 39, 40, and 41 with the previously prepared dataand senses and reports the change of processing characteristics withtime for a substrate to be processed or the cleaning time of the insideof the vacuum reactive chamber. The sense signal makes it possible toexternally grasp the change of the diameter of the trench bottomdependent on the number of substrates processed in processing a trenchfor trench capacitor. Furthermore, the report signal enables thecondition and the like of the inner surface of the vacuum reactivechamber to be grasped indirectly from the outside, which makes itpossible to determine the suitable cleaning time of the inside of thevacuum reactive chamber.

[0060]FIG. 5 shows a magnetron RIE system, a type of dry etching systemaccording to a second embodiment of the present invention, and a controlcircuit for controlling the operation of the system.

[0061] The RIE system of the second embodiment differs from that of FIG.3 in an additional high-frequency power supply control circuit 43 thatreceives the sense signal outputted from the sense/report circuit 42 andcontrols the output of the high-frequency power supply 34.

[0062] In the RIE system of the second embodiment, on the basis of thesense signal outputted according to one or two or more of the value ofVpp measured by the Vpp measuring circuit 39, the value of Vdc measuredby the Vdc measuring circuit 40, and the value of the impedance measuredby the Z measuring circuit 41, the high-frequency power supply controlcircuit 43 is controlled. In addition, the output of the high-frequencypower supply 34 is controlled on the basis of the output of thehigh-frequency power supply control circuit 43. In this way, theimpedance Z, the peak-to-peak voltage Vpp of the high-frequency electricpower, and the self-bias voltage Vdc are controlled. Then, shape controlin processing a substrate can be performed by controlling the output ofthe high-frequency power supply 34 in such a manner that each of themeasured values is kept at a desired constant value.

[0063] After each lot processing of semiconductor substrates was carriedout using the RIE system of FIG. 5, a sample of the substrate as shownin FIG. 1A was placed in the vacuum reactive chamber. HBr gas, O₂ gas,and NF₃ gas were introduced as reactive gases through the branch paths27, 28, 29 into the vacuum reactive chamber at flow rates of about 100,10, and 70 sccm, respectively. Discharging plasma 24 was generated at apressure of about 200 mToor (about 26.6 Pa) in the vacuum reactivechamber with the output of the high-frequency power supply 34 beingapplied to the cathode electrode 23, thereby causing reactive ions toetch the sample.

[0064] At that time, dry etching was done changing the output (RF-Power)(W) of the high-frequency power supply 34, thereby examining how thepeak-to-peak voltage Vpp of the high-frequency signal changed. At thesame time, how the taper angle θ at the top of the trench as shown inFIG. 1B changed was also examined. The results are shown in FIGS. 6A and6B.

[0065] It can be seen from FIGS. 6A and 6B that the output of thehigh-frequency power supply 34 and the peak-to-peak voltage Vpp of thehigh-frequency signal and the taper angle θ of the trench haveone-to-one correspondence and therefore the taper angle θ can becontrolled by the high-frequency output.

[0066] The reason is not clear. The equation W=Vpp²/Z generally holds.When the amount of reaction products generated is almost constant, Z isalmost constant. Therefore, Vpp is proportional to W and the value ofVpp is estimated to be determined.

[0067] Furthermore, part of the reaction products adhere to the sidewallof the trench to make a sidewall protective film. The taper angle θ atthe top of the trench is controlled by the amount of the sidewallprotective film. As the sidewall protective film gets thicker, the taperangle θ becomes smaller.

[0068] In addition, since Vdc is generally equal to Vpp/2, an increasein Vpp increases Vdc, which increases the energy at which reactive ionsarrive at the substrate. As a result, the sidewall protective filminside the trench is estimated to be scraped away, making the taperstand more straight.

[0069] With the RIE system of the second embodiment, the value of Vpp ismeasured by the Vpp measuring circuit 39, the value of Vdc is measuredby the Vdc measuring circuit 40, and the value of Z is measured by the Zmeasuring circuit 41. The high-frequency power supply control circuit 43is controlled on the basis of the sense signal outputted from thesense/report circuit 42 according to the result of the measurements. Theoutput of the high-frequency power supply 34 is controlled to anarbitrary value in such a manner that the measured value of Vpp, Vdc, orZ is kept at a specific set value. Controlling the high-frequency powersupply circuit 43 and the output of the high-frequency power supply 34this way enables the shape of the trench to be controlled.

[0070]FIG. 7 shows a magnetron RIE system, a type of dry etching systemaccording to a third embodiment of the present invention, and a controlcircuit for controlling the operation of the system.

[0071] The RIE system of the third embodiment differs from that of FIG.1 in an additional gas flow-rate control circuit 44 that receives thesense signal outputted from the sense/report circuit 42 and controls theflow rate of each of the gases by controlling the opening and closing ofthe electronic valves 30, 31, 32. The output of the gas flow-ratecontrol circuit 44 is supplied to each of the electronic valves 30, 31,32.

[0072] In the RIE system constructed as described above, after each lotprocessing of semiconductor substrates, a sample of the substrate asshown in FIG. 1A was placed in the vacuum reactive chamber. HBr gas, O₂gas, and NF₃ gas were introduced as reactive gases through the branchpaths 27, 28, 29 into the vacuum reactive chamber. Discharging plasma 24was generated at a pressure of about 200 mToor (about 26.6 Pa) in thevacuum reactive chamber with the output (RF-Power) of the high-frequencypower supply 34 being applied to the cathode electrode 23, therebycausing reactive ions to etch the sample.

[0073] At that time, dry etching was done by introducing HBr gas and NF₃gas at flow rates of about 100 and 70 sccm respectively, and changing aflow rate of O₂ gas, thereby examining how the peak-to-peak voltage Vppof the high-frequency signal changed. At the same time, how the taperangle θ at the top of the trench as shown in FIG. 1B changed was alsoexamined. The results are shown in FIGS. 8A and 8B.

[0074] It can be seen from FIGS. 8A and 8B that the flow rate of the O₂gas and the peak-to-peak voltage Vpp of the high-frequency signal andthe taper angle θ of the trench have one-to-one correspondence andtherefore control can be performed on the basis of the flow rate of theO₂ gas.

[0075] The reason is not clear. The equation W Vpp²/Z generally holds.An increase in the flow rate of the O₂ gas increases the amount ofreaction products of the SiBr_(y)O₂ family generated, which increasesthe impedance Z. In this case, therefore, W is almost constant. Fromthis, the value of Vpp can be considered to have decreased.

[0076] Furthermore, since the magnitude of the impedance z depends onthe amount of reaction products, a similar effect is easily estimated tobe produced in a case where a process gas including a bromine-containinggas, such as HBr containing Br and F composing reaction products and afluorine-containing gas, such as NF₃, is used.

[0077] With the RIE system of the third embodiment, the value of Vpp ismeasured by the Vpp measuring circuit 39, the value of Vdc is measuredby the Vdc measuring circuit 40, and the value of Z is measured by the Zmeasuring circuit 41. On the basis of the results of the measurements,the gas flow-rate control circuit 44 is controlled and the valves 30 to32, particularly the valve 31 for controlling the flow rate of O₂ gas,are controlled. In this way, the flow rate of each process gas iscontrolled to an arbitrary value in such a manner that the measuredvalue of Vpp, Vdc, or Z is kept at a specific set value, which enablesthe shape of the trench to be controlled.

[0078] Next, a method of processing a substrate using the RIE system inFIG. 5 or 7 will be explained briefly by reference to a flowchart inFIG. 9.

[0079] When the processing of a substrate is started, the supply of eachprocess gas and the output of the high-frequency power supply are firststarted.

[0080] At least one of the measured values of the impedance Z of thepart including the system and plasma 24, the peak-to-peak voltage Vpp ofthe high-frequency signal applied to the plasma 24, and the self-biasvoltage Vdc developing at the cathode electrode 23 is taken in by thesense/report circuit 42.

[0081] Then, it is judged whether those measured values are equal to thepreviously set values. The judgment is made at the sense/report circuit42. If the measured value is equal to the set value, the supply of theprocess gas and the output of the high-frequency power supply arestopped at the time when the set process end time has been reached,which completes the process.

[0082] When the set process end time has not been reached, the measuredvalue is taken in again by the sense/report circuit 42, which judgeswhether the measured value is equal to the set value.

[0083] If the measured value is different from the set value, theprocess condition, such as the process gas or the output of thehigh-frequency power supply, is adjusted in real time. Then, it isjudged whether a measured value equal to the set value has beenobtained. At this time. If a measured value equal to the set value hasnot be obtained, a process stop signal is transmitted to thehigh-frequency power supply 34 or valves 30 to 32, which forces theprocess to end. At the same time, the sense/report circuit 42 outputsthe report signal that reports that the cleaning time has been reached.

[0084] Monitoring the impedance Z, peak voltage Vpp, and self-biasvoltage Vdc makes it possible to clearly grasp, from the outside of thevacuum chamber, the change of substrate processing characteristic in thevacuum chamber with time and the cleaning time of the inside of thevacuum chamber. In addition, keeping the result of monitoring at anarbitrary value enables shape control of processing, which makes itpossible to suppress the change with time.

[0085]FIG. 10 shows a magnetron RIE system, a type of dry etching systemaccording to a fourth embodiment of the present invention, and a controlcircuit for controlling the operation of the system.

[0086] The RIE system of the fourth embodiment differs from that of FIG.1 in an additional pressure control circuit 45 that receives the sensesignal outputted from the sense/report circuit 42 and controls thepressure in the vacuum reactive chamber by controlling the opening andclosing of the electronic valve 33 provided at the outlet 26. The outputof the pressure control circuit 45 is supplied to the valve 33.

[0087] After each lot processing of semiconductor substrates using theRIE system of the fourth embodiment, a sample of the substrate as shownin FIG. 1A was placed in the vacuum reactive chamber 21. Reactive gaswas introduced into the vacuum reactive chamber 21. Then, the inside ofthe vacuum reactive chamber was kept at a specific pressure and theoutput of the high-frequency power supply 34 was applied, therebygenerating discharging plasma 24, which causes reactive ions to etch thesample.

[0088] At that time, dry etching was done changing the pressure in thevacuum reactive chamber 21, thereby examining how the taper angle θ atthe top of the trench as shown in FIG. 1A changed. The results are shownin TABLE 1 and FIG. 11. TABLE 1 PRESSURE (mTorr) TAPER ANGLE θ (°) 10088.42 150 88.17 200 88.09

[0089] It can be seen from TABLE 1 and FIG. 11 that as the pressure inthe vacuum reactive chamber 21 decreases, the taper angle θ increases.The reason is considered as follows. As the pressure in the vacuumreactive chamber decreases, ions begin to have the same direction andthe frequency of collision between ions or between ions and otherparticles, such as atoms, decreases. As a result, because the kineticenergy accelerated by an electric field is not lost because ofcollisions, the energy at which ions arrive at the substrate increases,which produces the effect of scraping the sidewall protective filmeasily as when the output of the high-frequency power supply 34 isincreased.

[0090] Therefore, the taper angle θ can be controlled to a desired valueby inputting the sense signal from the sense/report circuit 42 to thepressure control circuit 45, adjusting the amount of exhaust from thevacuum reactive chamber 21 by controlling the opening and closing of thevalve 33 according to the output of the pressure control circuit 45,thereby adjusting and keeping the pressure in the vacuum reactivechamber 21 at a desired constant value.

[0091]FIG. 12 shows a magnetron RIE system, a type of dry etching systemaccording to a fifth embodiment of the present invention, and a controlcircuit for controlling the operation of the system.

[0092] In the RIE system of the fifth embodiment, a cooling gas intake51 is provided on the reverse side of the cathode electrode 23, or onthe opposite side to the surface on which a substrate 22 to be processedis placed. A cooling gas, such as He gas, is introduced through theintake 51. The cooling gas introduced through the intake 51 erupts fromthe surface of the cathode electrode 23 on which the substrate 22 isplaced, thereby cooling the substrate 22.

[0093] Furthermore, an electronic valve 52 for adjusting the flow rateof the cooling gas introduced through the intake 51 is provided at thecooling gas intake 51. The opening and closing of the valve 52 iscontrolled according to the output of the gas flow-rate control circuit53 that receives the sense signal outputted from the sense/reportcircuit 42. In general, the inside of the vacuum reactive chamber 21where discharging plasma is being generated is as high as about 120° C.The substrate 22 in the chamber is also at about the same temperature.When a cooling gas, such as He gas, is erupted toward the back of thesubstrate 22, the temperature of the substrate 22 is adjusted accordingto the flow rate of the cooling gas.

[0094] After each lot processing of semiconductor substrates using theRIE system of the fifth embodiment, a sample of the substrate as shownin FIG. 1A was placed in the vacuum reactive chamber 21. Reactive gaswas introduced into the vacuum reactive chamber 21. Then, the vacuumreactive chamber was kept at a specific pressure and the cooling gas wasintroduced through the valve 52, thereby lowering the temperature of thesubstrate 22 to a specific temperature. Thereafter, the output of thehigh-frequency power supply 34 was applied to the cathode electrode 23,thereby generating discharging plasma 24, which causes reactive ions toetch the sample.

[0095] At that time, dry etching was done changing the temperature ofthe substrate 22, thereby examining how the taper angle θ at the top ofthe trench as shown in FIG. 1B changed. The results are shown in TABLE 2and FIG. 13. The flow rate (pressure) of the cooling gas is shown as thevalues related to the temperature. TABLE 2 PRESSURE (Torr) TAPER ANGLE θ(°) 10 88.36 15 88.25 20 88.19

[0096] It can be seen from TABLE 2 and FIG. 13 that, as the pressure ofthe cooling gas increases, the taper angle θ increases. The reason isconsidered as follows. As the pressure of the cooling gas is increased,the temperature of the substrate drops, increasing the amount ofdeposits of reaction products (sediment and sidewall protective films),which produces the effect of decreasing the taper angle θ as when theflow rate of O₂ gas is increased.

[0097] Therefore, the taper angle θ can be controlled to a desired valueby adjusting and keeping the temperature of the substrate at a desiredconstant value.

[0098] As described above, with a semiconductor device manufacturingsystem according to the present invention, it is possible to externallygrasp the change of the diameter of the trench bottom with timedependent on the number of substrates processed in processing, forexample, a trench for trench capacitor and the condition of the innersurface and others of the vacuum reactive chamber, making it possible todetermine the suitable cleaning time of the inside of the vacuumreactive chamber and control the processing of the shape of a substrate,which thereby suppresses the change with time.

[0099] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A semiconductor device manufacturing systemcomprising: a vacuum chamber provided with a cathode electrode forholding a substrate to be processed and into which a reactive gas forgenerating discharging plasma by the application of a high-frequencyelectric power is introduced; a high-frequency power supply connected tosaid cathode electrode, for applying a high-frequency electric power tosaid cathode electrode; a measuring circuit connected to said cathodeelectrode, for measuring at least one of the impedance of a systemincluding said plasma, the peak-to-peak voltage of a high-frequencysignal applied to said plasma, and a self-bias voltage applied to saidcathode electrode; and a sense circuit for receiving the measured valuefrom said measuring circuit, and for sensing the change of processingcharacteristics with time for said substrate by comparing said measuredvalue with previously prepared data.
 2. The system according to claim 1,wherein said reactive gas is an etching gas for etching said substrateto be processed.
 3. The system according to claim 1, further comprisingan impedance matching circuit provided between said high-frequency powersupply and said cathode electrode of said vacuum chamber, for effectingthe impedance matching between the output of said high-frequency powersupply and a load on the high-frequency power supply.
 4. A semiconductordevice manufacturing system comprising: a vacuum chamber provided with acathode electrode for holding a substrate to be processed and into whicha reactive gas for generating discharging plasma by the application of ahigh-frequency electric power is introduced; a high-frequency powersupply connected to said cathode electrode, for applying ahigh-frequency electric power to said cathode electrode; a measuringcircuit connected to said cathode electrode, for measuring at least oneof the impedance of a system including said plasma, the peak-to-peakvoltage of a high-frequency signal applied to said plasma, and aself-bias voltage applied to said cathode electrode; and a reportcircuit for receiving the measured value from said measuring circuit,for sensing that said measured value has departed from a preset range,and for reporting the cleaning time of the inside of said vacuumchamber.
 5. The system according to claim 4, wherein said reactive gasis an etching gas for etching said substrate.
 6. The system according toclaim 4, further comprising an impedance matching circuit providedbetween said high-frequency power supply and said cathode electrode ofsaid vacuum chamber, for effecting the impedance matching between theoutput of said high-frequency power supply and a load on thehigh-frequency power supply.
 7. A semiconductor device manufacturingsystem comprising: a vacuum chamber provided with a cathode electrodefor holding a substrate to be processed and into which a reactive gasfor generating discharging plasma by the application of a high-frequencyelectric power is introduced; a high-frequency power supply connected tosaid cathode electrode, for applying a high-frequency electric power tosaid cathode electrode; a measuring circuit connected to said cathodeelectrode, for measuring at least one of the impedance of a systemincluding said plasma, the peak-to-peak voltage of a high-frequencysignal applied to said plasma, and a self-bias voltage applied to saidcathode electrode; and a control circuit for receiving the measuredvalue from said measuring circuit, for supplying an output based on saidmeasured value to said high-frequency power supply, and for controllingthe output of said high-frequency power supply in such a manner that themeasured value of said measuring circuit is kept at a specific value. 8.The system according to claim 7, wherein said reactive gas is an etchinggas for etching said substrate.
 9. The system according to claim 7,further comprising an impedance matching circuit provided between saidhigh-frequency power supply and said cathode electrode of said vacuumchamber, for effecting the impedance matching between the output of saidhigh-frequency power supply and a load on the high-frequency powersupply.
 10. A semiconductor device manufacturing system comprising: avacuum chamber provided with a cathode electrode for holding a substrateto be processed and a reactive gas intake and into which a reactive gasfor generating discharging plasma by the application of a high-frequencyelectric power is introduced through said intake; a high-frequency powersupply connected to said cathode electrode, for applying ahigh-frequency electric power to said cathode electrode; an electronicvalve provided at said intake in such a manner that the intake of saidreactive gas introduced into said vacuum chamber is controlled; ameasuring circuit connected to said cathode electrode for measuring atleast one of the impedance of a system including said plasma, thepeak-to-peak voltage of a high-frequency signal applied to said plasma,and a self-bias voltage applied to said cathode electrode; and a controlcircuit for receiving the measured value from said measuring circuit,for supplying an output based on said measured value to said valve, andfor controlling the operation of said valve in such a manner that saidmeasured value of said measuring circuit is kept at a specific value.11. The system according to claim 10, wherein said reactive gas is anetching gas for etching said substrate.
 12. The system according toclaim 11, wherein said etching gas includes O₂ gas and the operation ofsaid valve is controlled by said control circuit in such a manner thatthe intake of said O₂ gas introduced into said vacuum chamber ischanged.
 13. The system according to claim 10, further comprising animpedance matching circuit provided between said high-frequency powersupply and said cathode electrode of said vacuum chamber for effectingthe impedance matching between the output of said high-frequency powersupply and a load on the high-frequency power supply.
 14. Asemiconductor device manufacturing system comprising: a vacuum chamberprovided with a cathode electrode for holding a substrate to beprocessed, a reactive gas intake, and a reactive gas outlet, and intowhich a reactive gas for generating discharging plasma by theapplication of a high-frequency electric power is introduced throughsaid intake; a high-frequency power supply connected to said cathodeelectrode, for applying a high-frequency electric power to said cathodeelectrode; an electronic valve provided at said outlet in such a mannerthat the pressure in said vacuum chamber is adjusted; a measuringcircuit connected to said cathode electrode for measuring at least oneof the impedance of a system including said plasma, the peak-to-peakvoltage of a high-frequency signal applied to said plasma, and aself-bias voltage applied to said cathode electrode; and a controlcircuit for receiving the measured value from said measuring circuit,for supplying an output based on said measured value to said valve, andfor controlling the operation of said valve in such a manner that themeasured value of said measuring circuit is kept at a specific value.15. The system according to claim 14, wherein said reactive gas is anetching gas for etching said substrate to be processed.
 16. The systemaccording to claim 14, further comprising an impedance matching circuitprovided between said high-frequency power supply and said cathodeelectrode of said vacuum chamber for effecting the impedance matchingbetween the output of said high-frequency power supply and a load on thehigh-frequency power supply.
 17. A semiconductor device manufacturingsystem comprising: a vacuum chamber provided with a cathode electrodefor holding a substrate to be processed and into which a reactive gasfor generating discharging plasma by the application of a high-frequencyelectric power is introduced; a high-frequency power supply connected tosaid cathode electrode, for applying a high-frequency electric power tosaid cathode electrode; a cooling gas carrying path provided at saidcathode electrode and into which a cooling gas is introduced to coolsaid substrate; an electronic valve provided at said cooling gascarrying path in such a manner that the pressure of said cooling gasintroduced into said cooling gas carrying path is adjusted; a measuringcircuit connected to said cathode electrode, for measuring at least oneof the impedance of a system including said plasma, the peak-to-peakvoltage of a high-frequency signal applied to said plasma, and aself-bias voltage applied to said cathode electrode; and a controlcircuit for receiving the measured value from said measuring circuit,for supplying an output based on said measured value, and forcontrolling the operation of said valve in such a manner that themeasured value of said measuring circuit is kept at a specific value.18. The system according to claim 17, wherein said reactive gas is anetching gas for etching said substrate to be processed.
 19. The systemaccording to claim 17, further comprising an impedance matching circuitprovided between said high-frequency power supply and said cathodeelectrode of said vacuum chamber, for effecting the impedance matchingbetween the output of said high-frequency power supply and a load on thehigh-frequency power supply.
 20. A method of manufacturing semiconductordevices, comprising the steps of: causing a cathode electrode providedin a vacuum chamber to hold a substrate; generating discharging plasmain said vacuum chamber by introducing a reactive gas into said vacuumchamber and applying a high-frequency electric power to said cathodeelectrode; measuring at least one of the impedance of a system includingsaid plasma, the peak-to-peak voltage of a high-frequency signal appliedto said plasma, and a self-bias voltage applied to said cathodeelectrode; and sensing the change of processing characteristics withtime for said substrate by comparing said measured value with previouslyprepared data.